Roots-type machines in current use are limited as regards their flow-rates when working at high pressures, in particular due to their being coupled to primary pumps having flow-rates that are lower at high suction pressures, and also due to the limited power of their motors.
The use of starter systems servo-controlled to the working pressure of the primary pump and to the pressure difference between the suction portion and the delivery portion of the Roots machine has already been described. Such devices are costly and complicated, and are therefore unreliable. Moreover, servo-controlled systems require pressure to be tapped from the pumping line, and this suffers from major drawbacks, in particular for reasons of safety in the event that corrosive gases are being pumped.
An object of the invention is to provide an installation of the type mentioned in the introduction and enabling the pumping speed of the Roots machine to be automatically regulated by simple, compact, cheap, effective, and safe means.